1. Field
Embodiments of the present invention relate to an organic light emitting display and a driving method thereof.
2. Description of Related Art
Recently, various types of flat panel display with reduced weight and volume in comparison to a cathode ray tube display have been developed. The various types of flat panel display include a liquid crystal display, a field emission display, a plasma display panel, an organic light emitting display, etc.
Among others, the organic light emitting display displays an image using organic light emitting diodes that generate light by recombination of electrons and holes. Such an organic light emitting display can be driven at low power consumption with rapid response speed.
FIG. 1 is a schematic circuit view of a pixel 4 of an organic light emitting display in the related art.
Referring to FIG. 1, the pixel 4 of the organic light emitting display in the related art includes an organic light emitting diode OLED, and a pixel circuit 2 that is coupled to a data line Dm and a scan line Sn to control the organic light emitting diode OLED.
The anode electrode of the organic light emitting diode OLED is coupled to the pixel circuit 2, and the cathode electrode thereof is coupled to a second power supply ELVSS. Such an organic light emitting diode OLED emits light at a brightness corresponding to the current supplied from the pixel circuit 2.
When a scan signal is supplied to the scan line Sn, the pixel circuit 2 controls the amount of current supplied to the organic light emitting diode OLED corresponding to a data signal supplied to the data line Dm.
To this end, the pixel circuit 2 includes a second transistor M2 coupled between a first power supply ELVDD and the organic light emitting diode OLED, a first transistor M1 coupled to the data line Dm and the scan line Sn, and a storage capacitor Cst coupled between the gate electrode and the first electrode of the second transistor M2.
The gate electrode of the first transistor M1 is coupled to the scan line Sn, and the first electrode thereof is coupled to the data line Dm. The second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor Cst.
Herein, the first electrode is set to any one of the source electrode and the drain electrode, and the second electrode is set to the other electrode. For example, if the first electrode is set to the source electrode, the second electrode is set to the drain electrode. When the scan signal is supplied from the scan line Sn, the first transistor M1 is turned on to supply the data signal supplied from the data line Dm to the storage capacitor Cst. At this time, the storage capacitor Cst is charged with the voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor Cst, and the first electrode thereof is coupled to the other terminal of the storage capacitor Cst and the first power supply ELVDD. The second electrode of the second transistor M2 is coupled to the anode electrode of the organic light emitting diode OLED.
The second transistor M2 controls the amount of current flowing to the second power supply ELVSS from the first power supply ELVDD via the organic light emitting diode OLED, corresponding to the voltage value stored in the storage capacitor Cst. Here, the organic light emitting diode OLED generates light corresponding to the amount of current supplied from the second transistor M2.
However, the above described organic light emitting display in the related art has a problem that it cannot display an image with a desired brightness due to the change in efficiency of the organic light emitting diode OLED as it deteriorates.
As the organic light emitting diode OLED deteriorates over time, the brightness of light generated by the OLED is gradually lowered corresponding to the same data signal. Also, the related art has a problem that an image having a uniform brightness cannot be displayed due to non-uniformity in threshold voltage/mobility of the driving transistor M2 included in the respective pixels 4.
In order to solve the above described problems, it is known to extract the deterioration information of the organic light emitting diode, while supplying current to the organic light emitting diode, and extract the threshold voltage and mobility information of the second transistor M2, while sinking current.
However, when extracting the deterioration information of the organic light emitting diode and the threshold voltage information of the second transistor M2 using current, a problem arises in that information of pixels coupled to some scan lines is unstably extracted. More specifically, there is parasitic capacitance between the data lines and the pixels, wherein only when the parasitic capacitance are sufficiently charged, desired information can be extracted from the pixels. However, problems arise in that a predetermined time is required to charge the parasitic capacitance using current, and exact (or accurate) information cannot be extracted from the pixels where information is extracted during the charging time of the parasitic capacitance (actually, exact information is not extracted from the pixels where information is extracted at a timing relatively shorter than a time constant of the resistive component of the data line and the parasitic capacitance).